The present invention relates to a method of and a system for measuring the level of a liquid surface automatically by an image processing and, more particularly, to a position recognition of the liquid surface in a container such as a tank or of a dam or river by an image.
The measurement of the height of a liquid surface (i.e., the liquid surface) is to measure the distance from the reference horizontal surface to the surface of the liquid. In the prior art, this liquid-level measuring method by measuring a displacement length is divided, as described in Handbook of Mechanical Engineering (6th Edition, 1977 Japanese Mechanical Association, Volume 6 Measuring Method, Section 7-7.6 Measurement of Liquid Level), into a method of measuring the liquid level directly by means of the so-called hook gauge or point gauge and a method of floating a float on the liquid surface to measure the displacement of the float mechanically.
On the other hand, a measurement method by metering the pressure is divided into a method of mechanically or electrically detecting the deformation of a diaphragm attached to the bottom or side face of a tank and a method of inserting a capillary into a liquid to inject compressed air from the capillary tip and thereby measure the back pressure of the capillary.
On the other hand, the measurement of the water level or tide level in a dam, a trough gate or the bank or mouth of a river is generally effected by a method of reading a measuring plate by human eyes. As the mechanical method of measuring the water surface position, there is disclosed in the aforementioned publication a method in which the water is introduced from the river through a tunnel or the like into a well in the ground so that the measurement is effected l with a float on the water surface.
The aforementioned mechanical liquid-surface detecting system of the prior art cannot avoid mechanical trouble because a mechanical structure is mounted on or in the water. Hence, the operator is periodically required to be present in order to ascertain that the meter is normal. This requirement conflicts with the need to minimize the patrol in case the site having its liquid surface confirmed is dangerous or remote.